Plasma treatment is known as a surface treatment method such as the cleaning and etching of a substrate on which electronic parts are mounted. In this plasma treatment, surface treatment such as cleaning is carried out by the etching action of plasma which is generated by mounting a substrate in a treatment chamber in a reduced-pressure atmosphere and by causing plasma discharge to take place in the treatment chamber. A substrate guide mechanism is provided for guiding the substrate during its carrying-in and carrying-out and for holding the substrate in a proper position and attitude during plasma treatment (e.g., refer to Japanese patent publications JP-A-10-140376 and JP-A-10-223725).
In JP-A-10-140376, a side end surface of the substrate is guided by a bar-shaped guide member arranged in a substrate transporting direction, and the mounting position of the guide member is changed in correspondence with the widthwise dimension of the substrate which serves as the object. In addition, in JP-A-10-223725, an electrode which also serves as a mounting portion on which the substrate is mounted is fabricated in a shape capable of guiding a side end portion of the substrate, and each time the substrate serving as the object is changed, the mounting portion is replaced in conformity with the substrate.
In recent years, resin substrates have come to be increasingly used as mounting substrates. Since the resin substrate is thin and deflectable, the resin substrate has a characteristic that a gap can possibly be formed between the resin substrate and the electrode with the resin substrate mounted thereon, so that a malfunction such as an abnormal discharge is likely to occur. For this reason, in a plasma treatment apparatus using such a resin substrate as an object, an arrangement has come to be used in which an upper surface of the electrode on which the substrate is mounted is covered with a material which is difficult to generate a discharge, such as a ceramic for the purpose of preventing the abnormal discharge.
However, in the plasma treatment apparatus having the arrangement in which the upper surface of the electrode is thus covered with the ceramic, if the substrate guide mechanism such as the one described above is adopted, the following malfunction is encountered. Namely, if a ceramic guide body is attached by bolting on each such occasion, since the ceramic is an extremely brittle and a breakable material, the guide member is easily broken at the bolted portions and cannot withstand repeated use, so that this arrangement is difficult to be adopted in practical use.
In addition, if the method shown in the patent document 2 is adopted, a ceramic-made mounting portion must be prepared for each kind of substrate, so that a rise in the running cost is unavoidable. Thus, in the conventional plasma treatment apparatuses, there has been a problem in that in the case where a thin-type substrate such as a resin substrate is used as an object, it is difficult to realize a substrate guide mechanism which is effectively capable of preventing an abnormal discharge.